The use of an electric heating element, in which electric current is used for the resistive heating of a wire, incorporated in a warming unit to provide a heat source with a flat support surface is pervasive in modern kitchen appliances. One problem attendant with such warming units is localized heating phenomena resulting in "hot spots" that occur on the support surface of the heating unit. Since, in the case of conventional warming units, a cooking vessel placed on the support surface is primarily heated by thermal conduction over the base of the cooking vessel, it is not unusual for the base of the cooking vessel to have hot spots corresponding to those on the heating element surface which are at a much greater temperature than the average temperature of the cooking vessel base. Food or beverages contained in the vessel may accordingly become scorched or burned by these localized hot spots.
One particular type of apparatus to which the present invention is specifically directed are hot beverage brewing devices of the drip brew type, especially drip brew coffee makers. These devices encompass, for example, both multiple unit commercial coffee makers used in restaurants and institutional kitchens and single unit drip brew coffee makers currently marketed by a wide variety of manufacturers for home use. The coffee maker industry is of particular interest since there has been a rapid expansion of the use of coffee makers in the home, as well as in restaurants, over the last 20 years. Such coffee makers have, to a large extent, replaced percolating coffee pots, both electric and non-electric.
As is well known, the typical coffee maker includes a housing and a water heating unit which receives water and heats the water to a brewing temperature. This water is conveyed through a coffee-holding filter assembly, wherein the water becomes flavored by the coffee, and is then downwardly dispensed under the influence of gravity into a receiving vessel, preferably in the form of a glass coffee pot. The coffee pot receives and stores the brewed coffee from the coffee maker and traditionally rests on a warming unit, or hot plate, of the coffee maker. Such hot plates may have either a constant temperature heat element, normally operating in a range of 220.degree.-250.degree. F. or, in the alternative, a heat source cyclicaling between an "on" state and an "off" state controlled, for example, by a timer or thermostat whereby the coffee remains at a fairly stable temperature range. Even on the cyclical systems, however, the heat element typically has temperature amplitude with a peak, or maximum, temperature in the "on" state that exceeds 250.degree. F. to compensate for those time periods when the source is in the off state.
Due to localized heating by both steady temperature and the cyclical heating elements, excessive temperatures at localized areas are transmitted by thermal conduction through the base of the containment vessel to that portion of the beverage adjacent thereto. This transmission of excessive heat causes a cooking action within coffee which degenerates attributes of the coffee, such as flavor, aroma, and color. Over a period of time, an increasing portion of the coffee is exposed to the excess temperatures. This is compounded by mixing of the coffee during removal of coffee containing vessel for pouring. Therefore, the stored coffee in the coffee pot becomes increasingly degraded over time.